La Tour du Valat

Institut de recherche pour la conservation des zones humides méditerranéennes

Titre :	Hosts feeding only Brown-headed Cowbird fledglings: where are the host fledglings?
Auteurs :	Justin L. Rasmussen, Auteur ; Spencer G. Sealy, Auteur
Type de document :	Article
Dans :	Journal of Field Ornithology (77(3) SUM 2006)
Article en page(s) :	269-279
Langues:	Anglais
Résumé :	Brown-headed Cowbirds (Molothrus ater) impose costs on their hosts, usually resulting in fewer or no host young being raised. In 95% of the studies where attempts were made to estimate the cost of parasitism, cost was measured as the difference in host nestling survival in parasitized and unparasitized nests. For hosts that fledge at least some of their own young along with cowbirds, the magnitude of further brood reduction beyond the nestling stage is not known. To examine the possibility that further brood reduction occurs during the fledgling stage, we compiled 102 observations of 45 species feeding fledgling cowbirds. In 97 cases, observers did not record hosts feeding their own young, suggesting that many young die shortly after fledging from parasitized nests. These observations suggest that measuring the cost of parasitism as the difference between the number of host young fledged from parasitized and unparasitized nests probably overestimates the reproductive output of many hosts. If costs increase during the fledgling stage, then the costs of brood parasitism have been underestimated in many studies.

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